WineGeo: Grès des Vosges

The wines of Alsace are a white wine lover’s dream…dry, powerful Rieslings, spicy Pinot Gris, and aromatic Gewurztraminer are just a few of the amazing white wines that are produced in Alsace. (Shout out to the Pinot Noir for red wine lovers as well.)

The soils of Alsace are just as diverse; as a matter of fact, according to the website of Wines of Alsace, “The terroir of Alsace is a geologist’s dream…if you walk 100 feet in any direction, you’ll find a different soil composition, making Alsace a complex mosaic unlike any other wine region.”

Soils underlying the vineyards in Alsace range from the schist and granite of the higher elevations (extending into the Vosges Mountains) to the limestone and chalk of the lower slopes, to the clay and gravel of the valley floors. However, it is the unique, reddish-colored sandstone of Alsace—known as grès des Vosges—that inspired this post.

For starters, grès des Vosges (Vosges sandstone) runs in a large, horizontal swath through the Vosges, underneath a granite layer (from which it is derived) and atop a layer of coal. Grès des Vosges is a hard, compact sandstone composed mainly of quartz and feldspar. Its pink-reddish color is due to the presence of decomposing iron (iron oxide, as also seen in red soils such as terra rosa) that occurred as a result of the slow cooling of large masses of magma as it hardened into granite.

The process of the coloring of the sandstone is termed rubefaction. Much of the sandstone in the Vosges is still grey, and some is still undergoing the process of rebefaction (or rebéfaction as they say in French).

The Strasbourg Cathedral, widely considered to be among the finest examples of late Gothic architecture, is partially composed of grès des Vosges, which gives the building its pink-hued appearance. The Strasbourg Cathedral was the tallest building in the world from 1647 to 1874 (227 years). Today, it remains the sixth tallest church in the world and the tallest existing structure built entirely in the Middle Ages.

Carte topographique des Vosges by Boldair, via Wikimedia Commons

Grès des Vosges is considered a unique aspect of the Vosges Mountains and Alsace—so much so that it has earned Protected Geographical Indication status from the EU. It is also still in great demand as a building material, and as such there is also a trade organization, the Union des Producteurs de Grès des Vosges, built around promoting and protecting the stone.